During the wrapping of pulp bales by means of two wrapping sheets, precut sheets or rolls are presently used, from which the sheets are cut in connection with the wrapping process. One sheet is thus transported to a lower folding position in a lower sheet pocket, and the other sheet is transported to an upper folding position in an upper sheet pocket. The sheets are positioned in such a way that, when the pulp bale is transported by a conveying belt between an upper and a lower conveyor, it comes into contact with the two sheets, whereby one on the upper side and one on the lower side of the bale follow along with the bale between the conveyors.
The lower wrapping sheet is clamped between the bale and the lower conveyor and in this way follows along with the bale in between the conveyors.
The bale height, however, can vary. In order to nevertheless ensure that the upper wrapping sheet in this case is also clamped between the bale and the upper conveyor, this conveyor has been inclined in such a way that the distance between the upper and lower conveyor decreases along the direction of transport.
The upper conveyor has thus been made resilient in such a way that a sufficient contact force is obtained, and the upper wrapping sheet thus follows along with the bale when the sheet is clamped between the upper conveyor and bale. The force, however, must not be so great that the bale is rigidly clamped and obstructed with continued passage between the conveyors.
While the bale together with the applied wrapping sheets is transported between the upper and lower conveyors, the sides of the sheet parallel to the conveying direction are folded inward towards the bale, and thereafter the bale is transported to a folding machine by a conveyor.
The problem with the present technology is that the upper and lower wrapping sheets, when the folding process is to commence, can be offset in relation to each other in the conveying direction. This displacement varies with the bale height and, thus, differs from one bale to the next. The displacement of the wrapping sheets can thus create problems in subsequent folding machines.
In the case above, the upper conveyor is inclined and the bale height varies, the point where the bale comes into contact with the upper conveyor for clamping the wrapping sheet can vary considerably. As a result, the upper sheet is displaced in relation to the lower sheet, because the lower sheet is always clamped at the same distance from the edge of the wrapping paper, while the upper sheet is clamped at different distances from the edge of the wrapping paper, depending on how far into the machine the bale has been transported before the bale comes into contact with the conveyor.
Due to the inclination of the upper conveyor, the contact force ensuring that the wrapping sheet is clamped is directed in such a manner that the bale is subjected to shearing forces. This, too, results in displacement of the wrapping sheets.
Another reason for such sheet displacement is that the conveyors advance the bale with varying force.